Question

This program should display 1 normal button (a) and 3 radio buttons (x,z,y). When the user selects one radio button and press the button a, it should redirects him to a website. The problem is during the launch. The window is empty, and in the bottom left there’s a message saying “Start: Applet Not Initialized”. Also, I get “java.lang.InstantiationException” in the console.

I’ll be grateful for any help.

package nome.nonoriginale;

import java.awt.Button;
import java.awt.Checkbox;
import java.awt.event.ActionListener;
import java.net.MalformedURLException;
import java.net.URL;

import javax.swing.JApplet;

import com.sun.corba.se.spi.orbutil.fsm.Action;

public abstract class Linkers extends JApplet implements ActionListener
{
Button a = new Button("Go to");

URL libro1;
URL libro2;
URL libro3;

Checkbox x;
Checkbox z;
Checkbox y;

public void init()
{
    try
    {
        libro1 = new URL("http://www.reddit.com/");
        libro2 = new URL("http://www.youtube.com/");
        libro3 = new URL("http://www.ismatteirecanati.it/default.aspx?pag=0&lang=it");
    }
    catch(MalformedURLException e)
    {
        System.out.println("Link's broken, brah");
    }
    add(a);
    add(x);
    add(z);
    add(y);

    a.addActionListener(this);
}

public void ActionPerformed(Action e)
{   
    if(x.getState() == true)
        getAppletContext().showDocument(libro1);

    else if(y.getState() == true)
        getAppletContext().showDocument(libro2);

    else if(z.getState() == true)
        getAppletContext().showDocument(libro3);
}

}

Answer 1

The class can’t be instantiated as it is declared abstract. You need to remove the abstract keyword from the class declaration:

public class Linkers extends JApplet implements ActionListener

Aside from that, you can implement ActionListener by implementing:

public void actionPerformed(ActionEvent e) {

It looks like you have imported a CORBA Action class by mistake.

Once these changes are made you wil get a NullPointerException as your checkboxes are not instantiated.

Don’t mix AWT with Swing components—AWT are heavyweight and will adversely affect the drawing of Swing components.

so you could use:

JCheckBox x = new JCheckBox();